Substrates, such those used for fabricating semiconductor, data storage, flat-panel display, and optoelectronic devices, are supported for processing in vacuum (i.e., low-pressure) chambers on chucks that typically include clamps for securing the substrates. Some substrate processing operations such as physical and chemical vapor deposition processes benefit from controlled thermal transfers between the chucks and the substrates. A gas sealed between the chucks and substrates is often used as a conductive medium for enhancing the thermal transfers and for regulating the substrate temperature during both active heating and cooling operations.
Low-pressure processing operations including device fabrication processes take place in vacuum (low-pressure) chambers that include chucks for supporting substrates in near vacuum or other low-pressure environments. Typical operating pressures for low-pressure fabrication processes such as physical-vapor deposition (PVD) and chemical-vapor deposition (CVD) range from less than 0.1 mTorr to more than 10.0 Torr. Some substrate chucks merely provide a substrate support platform and rely on substrate weight to hold the substrates in place. Most chucks, however, actively secure the substrates in process positions with either mechanical or electrostatic clamps.
Some chucks are also involved with the processing of the substrates by producing electrical or magnetic fields and/or by regulating heat transfers to or from the substrates. Electrical fields (e.g., produced through radio-frequency or xe2x80x9cRFxe2x80x9d bias) can be used to generate or enhance a plasma as well as to direct plasma ions and control the energy of ions impinging on the substrate. Magnetic fields can also be used to influence the plasma or to magnetically orient magnetic films during plasma-assisted depositions or thermal annealing. Heat transfers can be used either to remove excess heat from the substrates produced during processing operations or to provide a controlled amount of substrate heating for assisting other processing operations. Some processing operations are best performed at fixed substrate temperatures or at substrate temperatures that are adjusted throughout different stages of the operations. During operations like thermal annealing and thermal chemical vapor deposition (CVD) processes, elevated substrate temperatures activate or actually accomplish the substrate processing.
Thermal deposition and thermally activated processes such as chemical-vapor deposition (CVD), metal-organic chemical-vapor deposition (MOCVD), and thermal annealing processes also require active substrate heating (e.g., up to 350xc2x0 C.). Even higher substrate temperatures (e.g., up to 450xc2x0 C.) may be required for physical-vapor deposition (PVD) reflow depositions of interconnect materials (e.g., Al or Cu) for void-free filling of high-aspect-ratio structures. While some plasma sputtering operations require active heating of substrates, other plasma sputtering operations may require active cooling of the substrates. Some thermal deposition processes such as MOCVD of high-dielectric constant BST materials may require chucks for active heating of substrates to temperatures as high as 650xc2x0 C. On the other hand, some fabrication processes such as some plasma etch processes require active substrate cooling to temperatures as low as xe2x88x9240xc2x0 C.
However, controlling substrate temperatures in near vacuum or other low-pressure environments (e.g., process pressures below 1.0 Torr) is quite difficult because heat does not transfer well between objects in such environments. For example, the conduction of heat between contiguous surfaces of a chuck body and the substrate in a low-pressure environment is slow and inefficient (resulting in large temperature offsets) because actual contact on an atomic scale between their surfaces is limited to a small fraction of their common areas, and gaps that separate the remaining common areas of their surfaces are sufficient to prevent effective heat transfer by thermal conduction.
Heating and cooling of substrates through radiational heat transfers are possible in low-pressure environments, particularly at elevated substrate and/or chuck temperatures; but radiational heat transfers are generally too slow at lower temperatures to maintain substrates at desired processing temperatures. Below 500xc2x0 C., which includes most chuck-based fabrication processes, radiational heat transfers are generally too inefficient to regulate substrate processing temperatures effectively and quickly.
Faster transfers are possible by introducing a gas, preferably an inert gas such as helium or argon or another suitable gas such as nitrogen or hydrogen, between the chuck body and the substrate. Although still at much less than atmospheric pressure (e.g., 1 Torr to 20 Torr), the gas (referred to as a xe2x80x9cheat-transferxe2x80x9d or xe2x80x9cbacksidexe2x80x9d gas) sufficiently fills the small gaps and voids between the chuck body and the substrate to support significant heat transfer by thermal conduction between them. A seal formed between the mounting surface of the chuck body and a back surface of the substrate resists leakage of the gas into the rest of the processing chamber, which could disturb substrate processing operations.
U.S. Pat. No. 4,680,061 to Lamont, Jr. and U.S. Pat. No. 4,949,783 to Lakios et al. disclose examples of chucks that promote such heat transfers between chuck bodies and substrates using a heat-transfer gas. Lamont, Jr. traps the gas in a shallow cavity between a chuck body and a substrate using a raised rim seal that projects from a mounting surface of the chuck body into engagement with a back surface of the substrate. Lakios et al. disclose a similar sealing structure but provide for circulating the gas through the cavity for removing excess heat from the substrate by both thermal conduction and forced thermal convection.
Although the raised rim seals of Lamont, Jr. and Lakios et al. circumscribe large interior portions of their substrates"" back surfaces, the remaining portions of the back surfaces, which are engaged by their raised rim seals or which lie beyond the seals, are not exposed to the heat-transfer gas in the same manner as the more interior portions of the back surfaces. This can result in temperature gradients approaching their substrates"" peripheries and in processing nonuniformities of corresponding peripheral regions on their substrates"" front surfaces. Also, mechanical clamps of Lamont, Jr. and Lakios et al. engage the peripheral portions of their substrates"" front surfaces, effectively blocking the engaged portions from effective processing due to an exclusion zone.
Accordingly, the usual practice has been to define a peripheral exclusion zone on the front surfaces of substrates, which must subsequently be discarded as unusable for device fabrication. Considering the high cost of substrate manufacture, considerable savings can be realized by reducing or eliminating the exclusion zone and fabricating active devices over the entire front surfaces of substrates.
This invention utilizes peripheral edge surfaces of substrates, which are located between the front and back surfaces of substrates, for alternative or combined purposes of sealing and clamping the substrates to chuck bodies within low-pressure processing chambers. Peripheral edge seals can be arranged as either (a) primary seals to prevent significant leakage of heat-transfer gas into a surrounding processing region of the processing chambers while exposing substantially the entire back surfaces of substrates to the gas at a higher pressure than the process pressure of the surrounding region or (b) secondary seals in conjunction with separate primary seals to further reduce such leakage. Peripheral edge clamps, which can also function as the peripheral edge seals, can be arranged to engage front edges of the substrates"" peripheral edge surfaces for both (a) clamping the substrates against the chuck bodies and (b) centering the substrates on the chuck bodies while exposing substantially the entire front surfaces of the substrates to processing for extended front surface process coverage.
One embodiment of the invention envisioned as a low-pressure processing chuck includes a chuck body for supporting a substrate within an evacuatable space of a low-pressure processing chamber. The substrate has a front surface, a back surface, and a peripheral edge surface interconnecting the front and back surfaces. A sealing structure engages the peripheral edge surface of the substrate and together with the substrate and the chuck body forms a separately pressurizable region within the evacuatable space of the lowpressure processing chamber.
Preferably, the chuck body includes a mounting surface that together with the back surface of the substrate forms a heat-transfer interface, which itself comprises a first part of the separately pressurizable region. A second part of the separately pressurizable region surrounds the first part of the separately pressurizable region and isolates the first part of the separately pressurizable region from a processing region of the low-pressure processing chamber.
A control system can be used to direct a free (or essentially uninhibited) flow of heat-transfer gas between the two parts of the separately pressurizable region for exposing substantially the entire back surface of the substrate to the pressurized heat-transfer gas. Alternatively, the two parts of the separately pressurizable region can be separated by a seal, and the control system can be arranged to separately regulate pressures (or flows) in the two parts. For example, pressures in the second part of the separately pressurizable space can be reduced with respect to pressures in the first part of the separately pressurizable space for minimizing leakage of the heat-transfer gas from the first part of the separately pressurizable space into the processing region of the low-pressure processing chamber.
Envisioned specifically as a sealing structure, the invention provides at least part of a connection between the substrate and the chuck body for forming the separately pressurizable region within the low-pressure processing chamber. The sealing structure has a seal body with two sealing regions. The first sealing region contributes a portion of a first seal for connecting the seal body at least indirectly to the chuck body or an extension of the chuck body, and the second sealing region contributes a portion of a second seal that engages the peripheral edge surface of the substrate for connecting the seal body to the substrate.
Preferably, the second sealing region forms a full peripheral seat that engages the entire periphery of the substrate""s peripheral edge surface. The full peripheral seat preferably conforms to the shape of the substrate""s peripheral edge surface (e.g., circular or square for circular or square substrates) including reference features formed in the surface (e.g., flats or notches). Extended finger portions could also be used to cover localized reference features such as notches. The seat is also preferably shaped to expose substantially the entire front surface of the substrate for processing within the low-pressure processing chamber for the purpose of full-face coverage or near full-face coverage processing. However, the seat can also be shaped to prevent unwanted deposition of processing material at the second seal (for instance, to prevent sticking of the second seal to the substrate in a PVD process).
In addition to functioning as a seal, the sealing structure can also perform centering and clamping functions. For example, the second sealing region can also be shaped (e.g., as a truncated cone or pyramid) for centering the substrate on the chuck body in response to relative movement between the seal body and the chuck body along a centerline of the chuck body. An inclined surface of the second sealing region engages the peripheral edge surface of the substrate for guiding the substrate into a desired position on the chuck body.
The peripheral edge surface of the substrate includes a front edge adjacent to the front surface of the substrate and a back edge adjacent to the back surface of the substrate. The inclined surface of the second sealing region can engage either the front edge or the back edge of the peripheral edge surface for completing the second seal. When the front edge is engaged, the sealing structure can also function as a clamp for pressing the substrate against the chuck body. However, when the back edge is engaged, a separate clamping device, such as a mechanical or electrostatic clamp, is preferably used to secure the substrate to the chuck body (particularly when active heating or cooling of the substrate is required).
The invention can be arranged to perform the clamping function either independent of or in conjunction with the sealing function. Envisioned as a clamp, the invention includes a clamp body that is relatively translatable with respect to the chuck body along a central axis or centerline of the chuck body. An inner engaging region has an inclined seating surface that contacts the front edge of the peripheral edge surface for guiding the substrate into a desired position on the chuck body in response to the relative movement between the clamp and chuck bodies along the chuck body centerline.
The inner engaging region is preferably shaped to expose substantially the entire front surface of the substrate for full-face coverage or near full-face coverage processing within the low-pressure processing chamber. However, the inner engaging region can also be arranged to overhang a portion of the front surface of the substrate to prevent unwanted deposition of processing material at an interface between the inclined seating surface and the front edge of the substrate (for instance, to prevent sticking of the clamp to the substrate in a PVD process).
In the absence of the substrate, the inclined seating surface can be arranged to engage a mating surface on the chuck body for centering the clamp body on the chuck body for improved waferhandling reliability. Any mismatch between the surfaces of the clamp and the chuck body can be corrected in advance of processing to assure that the substrates are appropriately centered on the chuck body in order to eliminate the possibility of substrate misprocessing or robotic handling failures.
The inclined seating surface of the clamp can be a discontinuous surface for purposes of clamping but is preferably arranged as a full peripheral seal for also performing a sealing function. The clamp body is also preferably arranged to form another full peripheral seal with the chuck body to isolate a separately pressurizable region within the low-pressure processing chamber.